1. Field of the Invention
The invention generally concerns a method of applying and individualising or personalising a security element to a substrate or document.
Individualised, invariable security elements serve to protect the document provided therewith from unauthorised copying, from forgeries or from unauthorised alterations in the document.
2. Description of the Prior Art
European patent application No. EP 401 466 discloses a security element in the form of a composite laminate, for sticking onto a document. The laminate has diffraction structures which are embedded between a stabilisation layer and a thermally activatable adhesive layer. Transfer of the laminate onto the document is effected by a procedure whereby heat is supplied to the adhesive layer through the laminate, in which case the stabilisation layer uniformly distributes the heat and prevents locally excessive heating of the layers of lacquer which carry the diffraction structures. The composite laminate serves as a security element because of its optical effects which are produced by the diffraction structures.
EP 401 466 further discloses the formation of locations which have good and poor adhesion on the adhesive layer. In the thermal activation operation, an adhesive bond is formed between the composite laminate and the document, only at the locations which afford good adhesion. In the event of an attempt being made to detach it from the document, on the one hand the security element is destroyed. On the other hand, pieces of the security element remain behind on the document, according to the pattern of the adhesive bridge portions. The pattern which remains behind may be a pattern which has a meaning and for example may represent the word "VOID".
PCT application No. WO 93/16888 discloses a printing process for forming the adhesive layer of a composite laminate with locations which have good and poor adhesion. After the laminate has been transferred onto the document the carrier foil is pulled off again, in which case the carrier foil is detached from the laminate at the locations thereof which have good adhesion on the document, while at the locations which have poor adhesion the entire laminate is detached from the document. The parts of the laminate which remain behind on the document are in part finely structured images and cannot be removed from the document without leaving visible traces behind. Such parts may for example be present as fine lines on a photograph so that the photograph is clearly visible between the parts representing the security element.
Japanese Patent Abstract Vol. 15, No. 362 (M-1157) discloses a method in which a thermoplastic foil is applied to a chip card, as a scratch-proof protective layer. In order to prevent the foil from being subsequently peeled off, the surface of the chip card, which has an adhesive layer, is heated at critical locations by means of a laser beam which passes through the foil, to such an extent that the chip card, the adhesive layer and the foil are welded together.